Comprehensive characterization of the cis-regulatory code responsible for the spatio-temporal expression of olSix3.2 in the developing medaka forebrain

[Background] Embryonic development is coordinated by sets of cis-regulatory elements that are
collectively responsible for the precise spatio-temporal organization of regulatory gene networks.
There is little information on how these elements, which are often associated with highly conserved
noncoding sequences, are combined to generate precise gene expression patterns in vertebrates.
To address this issue, we have focused on Six3, an important regulator of vertebrate forebrain
development.[Results] Using computational analysis and exploiting the diversity of teleost genomes, we identified
a cluster of highly conserved noncoding sequences surrounding the Six3 gene. Transgenesis in
medaka fish demonstrates that these sequences have enhancer, silencer, and silencer blocker
activities that are differentially combined to control the entire distribution of Six3.[Conclusion] This report provides the first example of the precise regulatory code necessary for
the expression of a vertebrate gene, and offers a unique framework for defining the interplay of
trans-acting factors that control the evolutionary conserved use of Six3.